Mice deficient for p66shc have been generated previously and shown to have extended lifespan in one particular strain background (Migliaccio et al., 1999). Because p66shc deficiency is one of the few genetic interventions reported to increase lifespan in a mammal, studies to understand how this pathway impacts lifespan have the potential to increase our understanding of aging mechanisms. We have used gene targeting to generate mice that lack p66shc. This animal model was generated by selectively deleting a region of exon 2 of the p66shc gene in embryonic stem (ES) cells. We propose to use the newly generated p66shc mice to conduct a detailed study of the role of p66shc on the aging process. The central hypothesis to be tested is that p66shc deficiency will retard the aging process, and that this effect is due to reduced ROS levels, maintenance of mitochondrial function and reduced ROS-induced apoptosis during aging in target tissues. Using skeletal muscle as a model, we will test if p66shc deficiency will prevent age-related mitochondrial dysfunction, apoptosis, and age-related transcriptional alterations. Further, we propose to determine the effect of p66shc mutation on lifespan and disease patterns in a long-lived mouse genetic background. A previous study has provided preliminary experimental support for an association between p66shc deficiency and retardation of the aging process. In particular, p66shc deficient mice were shown to live approximately 30% longer (average lifespan) in a 129Sv genetic background. Because p66shc is the only reported mutation in mammals that may be able to extend lifespan in the absence of multiple endocrine disruption, a detailed characterization of mice lacking p66shc is needed. p66shc deficient animals, which are the focus of this application, should allow detailed characterization of the specific role of p66shc in longevity, its relationship to ROS mediated aging phenotypes, and a specific examination of the role of p66shc in skeletal muscle aging. We expect that this animal model will provide an extremely valuable tool to investigate the role of oxidative stress and apoptosis in aging. Aging rates will be evaluated at three levels: 1) organismal level by survival and disease patterns;2) biochemical and cellular level by measures of mitochondrial function, oxidative stress and apoptosis in skeletal muscle;and, 3) transcriptional level, through gene expression profiling in skeletal muscle.